Deterioration of stressed oxides: Application to the prediction of a non-volatile memory cell endurance

This paper investigates a new way of predicting an electrically erasable programmable read only memory (EEPROM) cell's endurance without stressing the cell itself. Tunnel equivalent capacitors, formed by silicon dioxide thermally grown on N+ type Si substrates and then covered with polycrystalline silicon, undergo dynamic stress made up of one million rectangular pulses. Then, Fowler-Nordheim parameters α and β are obtained after a few numbers of applied pulses. EEPROM model simulation with extracted α and β shows closure of programming window as number of cycles varies from 1 to 106. Comparison between simulated closure of programming window and measured closure of programming window from EEPROM endurance tests shows that simulated programming window closure is greater, especially at smaller numbers of write/erase cycles. This greater severity is attributed to tunnel oxide degradation due to additional stress caused by Fowler-Nordheim current measurement. We also compare the deterioration of the tunnel oxide caused by successive writings and the deterioration caused by successive erasings, which are found to be of the same amount.